1. Field of the Invention
This invention relates to a telephone exchange system, which accommodates a large number of office and private line trunks with respect to the number of accommodated terminals.
2. Description of the Related Art
FIG. 61 shows a prior art telephone exchange system.
The telephone exchange system shown in FIG. 61 includes a speech channel switch (SW) 611. To the speech channel switch 611 are connected line circuits (LIN) 613 which accommodate and control connection of telephone terminals 612 such as telephone sets and also trunks (TRK) 614 which accommodate and control connection of office and private lines.
A central controller (CC) 615 controls the entire telephone exchange system and also controls calls between two telephone terminals 612 and also between a telephone terminal 612 and an office or private line trunk. A memory (MM) 616 stores programs, office data and various tables used by the central controller 615 for the control of the telephone exchange system, and it is connected to the central controller 615 via a control system bus 617. The speech channel switch 611 is connected to the control system bus 617. Further, although not shown, the central controller 615 is logically connected to the extensions 613 and trunks 614. Thus, the speech channel switch 611, extensions 613 and trunks 614 are operable under control of the central controller 615.
One of the purposes of the usual telephone exchange system is to accommodate trunks matched in number to the number of calls. Therefore, in the above structure, the number n of the accommodated terminals 612 and the number m of the accommodated office and private lines (i.e., number of the trunks 614) are usually related as n&gt;m.
However, in a telephone exchange system adopted by financial organizations, such as banks and brokerage houses (also called a dealing speech system) for communication between a dealer and a customer to effect transactions (hereinafter referred to as dealings) of foreign exchanges and bonds, trunks are accommodated independently of the number of calls but in number corresponding to the number of the customers. This is so in that when a transaction occurs, a dealer has to instantly select and communicate with particular customers among a large number of customers.
Therefore, in a telephone exchange system used for dealing, the relationship between the number n of the accommodated telephone terminals 612 and number m of the accommodated trunks 614 in FIG. 61 is n&lt;m.
Such a large number of trunks may be accommodated in a large scale telephone exchange system (private branch exchange). In this case, however there is a problem of high probability that all communications in the telephone exchange system are interrupted at some time by some trouble.
Moreover, in a large scale telephone exchange system, the load on the central controller is large, and this requires a long time for connecting a call. These problems are most significant for a dealing business, in which prompt and accurate communication between the dealer and customer is necessary.